Friction, grit, or grid drive systems for moving strips or webs of sheet material longitudinally back and forth along a feed path through a plotting, printing, or cutting device are well known in the art. In such drive systems, friction (or grit or grid) wheels are placed on one side of the strip of sheet material (generally vinyl or paper) and pinch rollers, of rubber or other flexible material, are placed on the other side of the strip, with spring pressure urging the pinch rollers and material against the friction wheels. During plotting, printing, or cutting, the strip material is driven back and forth, in the longitudinal or X-direction, by the friction wheels while, at the same time, a pen, printing head, or cutting blade is driven over the strip material in the lateral or Y-direction.
These systems have gained substantial favor due to their ability to accept plain (unperforated) strips of material in differing widths. However, the existing friction drive apparatus experience several problems. One problem that occurs in friction drive apparatus is a skew error. The skew error will arise as a result of strip material being driven unevenly between its two longitudinal edges, causing the strip material to assume a cocked position. The error is integrated in the lateral or Y-direction and produces an increasing lateral position error as the strip material moves along the X-direction. The error is often visible when the start of one object must align with the end of a previously plotted object. In the worst case, such lateral errors result in the strip drifting completely off the friction wheel. The skew error is highly undesirable because the resultant graphic image is usually destroyed.
Most material strips are inserted manually into the friction drive systems. During the manual insertion, it is essentially impossible to place the material strip perfectly straight in the friction drive apparatus. Therefore, the existing systems typically use at least three feet of strip material until the strip material is straightened with respect to the friction drive apparatus. This manual alignment procedure has numerous drawbacks. First, it results in excessive material consumption and waste thereof. Second, the procedure is time consuming. Additionally, manual alignment is not always effective. Therefore, there is a need to reduce wasteful consumption of strip material during loading thereof into the friction drive apparatus and to ensure proper alignment of the strip material within the friction drive apparatus during operation.